How does the Sliding Length Windows work for JBoss BRMS ?

Issue

We have created the following rule that is using over window:length (Sliding Length Windows):

rule "Example"
   dialect "mvel"
   when
      Login( $login : login)
      Transacao( transactionType == "T1" , login == $login ) over window:length (5)
   then
      System.out.println("Rule was fired.");
   end

We have noticed that the rule is being fired every time that a T1 transaction type is encountered. The rule should fire only when inserted 5 instances of transaction type T1, shouldn't it ? If not, how does the Sliding Length Windows work for JBoss BRMS ?